The invention relates to a drive arrangement for an electric motor vehicle comprising an electric motor the output of which is controlled by means of a control rectifier, a transmission having at least two gears, a coupling associated with each of the gears in the transmission, an actuator which engages the couplings, and a control system which synchronizes the engagement of the coupling halves.
Generally, electric motor vehicles are equipped either with hand-operated multistage transmissions or with single-stage fixed transmissions. The latter have the disadvantage that a very large engine with correspondingly powerful components is required to achieve satisfactory road performance. Naturally, this affects weight and cost of the electric motor vehicle.
Multistage transmissions are generally larger and heavier than necessary (especially if they are adapted from the transmission of mass-produced combustion engine vehicles) because a transmission with only one or two forward gears is sufficient for an electric motor vehicle. Since the output of modern electric motors (magnitude and direction of rotation) can be controlled as desired by means of control rectifiers, a dedicated reverse gear is not needed.
In electric motor vehicles, it is desirable to have the lowest possible vehicle weight and the highest recovery of energy during braking because of the limited capacity of known storage batteries. Drive aggregates should therefore be as light as possible and take up as little space as possible since a vehicle will become heavier through increases in size alone. Furthermore, automatic transmissions are desirable since electric motor vehicles are mainly meant for city traffic. However, automatic transmissions have not been used heretofore in electric motor vehicles because of their high cost and low efficiency.
A two-gear transmission for electric motor vehicles where one or two free gears can be engaged via a multiple-disk clutch to the drive shaft is known from DE-A 42 12 324. Neither a dedicated reverse gear nor a separation coupling is provided in this transmission. The device which actuates the multiple-disk clutch does not have a neutral position. In a first step during the shifting process, a free wheel device is provided, not only to improve gear-shifting comfort, but mainly because otherwise the rapidly running electric engine together with its transmission would have to be accelerated to high velocity when shifting down into first gear.
This known transmission has, however, several disadvantages: Due to the utilization of friction clutch plates, the shifting process is relatively slow and fraught with considerable losses in energy--in the friction clutch itself and also because no recovery of energy during braking is possible because of the free wheel device, precisely when shifting down. Furthermore, the space requirement for the two multiple-disk clutches and therefore for the entire transmission is considerable.
A drive arrangement for an electric motor vehicle in which a separation coupling is automatically opened at the beginning of the shifting process and in which a computer receives signals indicative of engine RPM's and the gear which is engaged to produce an actuating signal is known from EP-B 21 877. The actuating signal produces a corresponding change in the engine RPM's as soon as the gear shift lever is in the new shifting position. Because of the direct manual gear shifting and the separation coupling, and in spite of the computer, the attainment of synchronization in the transmission itself is not ensured and mechanical synchronization with all its disadvantages must still be provided in this known transmission.
Finally, DE-A 36 05 377 discloses a drive arrangement suitable for any type of vehicle engine, having a multi-step reduction gear and a separation coupling, wherein the rotational speeds of the gears are synchronized with the driving engine by accelerating or decelerating the engine. This is done, however, with a disengaged separation coupling so that the part of the separation coupling on the transmission side and the part of the transmission on the input side must again be decelerated or accelerated by mechanical synchronization. In this drive, the special characteristics of an electric drive are not taken into consideration and the advantage to the driver is only minor.
It is therefore the object of the instant invention to provide a drive mechanism for an electric motor vehicle, and a method for shifting the gears of same which achieve the driving comfort of an automatic transmission with minimum constructive outlay and greatest economy.